There's two hot wires to the OBD port. One of them is always hot and the other is hot when the ignition is ON.
What I meant about the ECU grounding, is that there's no direct ground from the outside of the case. Everything is through the connectors.
As for the ECU being fried, if that be true, whatever caused it may still exist.
Couple of points: 1. I purchased an ECU that was laying on the cowl of the car in a Junk Yard. It had water standing in the two connection slots..... however, it was just fine! 2. Back about 4 years ago, when I was doing my ALH in the Vanagon, I accidently let a big hot wire drag across the outside case of the ECU. No problem, as it has served well over 70k miles.
I'd be concerned about the PO's hack job installing the stereo system. He may have cut wires for a power source that involved the OBD port and/or one of the three power wires coming out of the Relay 109 socket.